Layered He-4 in hectorite: A new quasi-two-dimensional environment for quantum liquids

We have studied the properties of quasi-two-dimensional He-4 in an environm ent provided by the layered structure of hectorite. A phase transition occu rs for areal densities between n = 0.029 Angstrom (-2) and n = 0.032 Angstr om (-2) where the structure of He-4 changes abruptly from a 4-layer to a 5- layer configuration. The signatures of this phase transition ar e detectabl e in the static density-density response function and in the density-depend ence of the roton minimum..